Invoking() should allow null subjects

[AVee]

Description

As per 15c20b3 the Invoking() methods are rejecting null subjects. While I fully agree with the check for the action, I feel that a null subject should be valid.

E.g. this seems a sensible test to write:

        public static void ThrowOnNull(object? arg)
        {
            if (arg == null)
                throw new ArgumentNullException(nameof(arg));
        }

        [Fact]
        public void ThrowsOnNull()
        {
            object? arg = null;
            arg.Invoking(x => ThrowOnNull(x))
                .Should()
                .Throw<ArgumentNullException>();
        }

Expected behavior:

The above test should succeed.

Actual behavior:

Currently this test fails, with an System.ArgumentNullException from within FluentAssertions.

Versions

FluentAssertions 6.2.0

[dennisdoomen]

The intention of Invoking is to invoke members of the subject-under-test. So we don't expect the subject itself to ever be null. But you can rewrite this as:

Action act = () => ThrowOnNull(arg);
act.Should().Throw<ArgumentNullException>();

[jnyrup]

Alternatively, this might fit your desire.

using static FluentAssertions.FluentActions;

Invoking(() => ThrowOnNull(null)).Should().Throw<ArgumentNullException>();